The rates of change in bone mass measured by total body neutron activiation continue on 140 normal men and women, 30-80 years of age. There data provide a base line for skeletal mass and lean body mass as a function of age. These data on bone loss continue to serve as a generalized model for aging research. The influence of exercise on aging related to bone loss continues. In a preliminary study to ascertain whether exercise could prevent involutional bone loss, 18 post menopausal women half of whom exercised three hours a week were studied. Total and regional bone mass were measured after one year of exercise. Total body calcium, measured by neutron activation, increased slightly but significantly. To obtain further data to support the hypothesis, that exercise can modify involutional bone and muscle loss, a study of 60 subjects was initiated. To date, 21 men and women have embarked on this planned program under supervision of a physical therapist and have completed six months with a mean increase in total body calcium of 3.1%. The difficulty, to data, has been in accruing a normal population of older subjects 60-80 years old, fit to participate in this program. People, so far, have had to be rejected on the basis of their physical indications of cardiovascular disease, osteoporosis and interfering medication. The program is continuing and we hope to recruit within the next year the total number of 60 normal mem and women for this study.